Running backs always get some opportunity, even if its just a few carries smattered in here and there. Like Choice, Shonn Green, Donald Brown, etc we will have a chance to see if he is good or not. Hell, all it takes is for Mendenhall to miss a couple of games and Dwyer only needs to be better than Frank Summers to get a decent load of work.
All of that being said, I have picks 5, 6, 13, and 20 and I think I would rather roll with McKnight around 13 and James Starks around 20 and let someone else play around with Dwyer.